CCC of science

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Across
  1. 1. something police have to do
  2. 4. something to back something up
  3. 6. a school subject
  4. 7. something you have hint:it starts with the letter p
Down
  1. 2. the ending of an argument
  2. 3. something you have with people
  3. 5. something you get from an article